
fancontrol - automated software based fan speed regulation


Introduction

fancontrol is a shellscript for use with lm_sensors. It reads its
configuration from a file, then calculates fan speeds from temperatures and
sets the corresponding pwm outputs to the computed values.  It is included in
lm_sensors since 2.8.0, the latest version is always available through SVN or
at http://www.hdev.de/fancontrol/ For easy configuration, there's a script
named pwmconfig which lets you interactively write your configuration file for
fancontrol. Alternatively you can write this file yourself using the
information from the configuration section of this document.

Please be careful when using the fan control features of your mainboard, in
addition to the risk of burning your CPU, at higher temperatures there will be
a higher wearout of your other hardware components, too. So if you plan to use
these components in 50 years, _maybe_ you shouldn't use fancontrol/your
hardware at all.  Also please keep in mind most fans aren't designed to be
powered by a PWMed voltage, for more detailed information on this I recommend
this appnote: http://www.maxim-ic.com/appnotes.cfm/appnote_number/707
In practice it doesn't seem to be a major issue, the fans will get slightly
warmer, just be sure to have a temperature alarm and/or shutdown call, in case
some fan fails, because you probably won't hear it anymore ;)

Configuration

Since most of you are going to use the prog/pwm/pwmconfig script, the config
file syntax will be discussed last. First I'm going to describe the various
variables available for changing fancontrol's behaviour:

INTERVAL
	This variable defines at which interval in seconds the main loop of
	fancontrol will be executed

FCTEMPS
	Maps pwm outputs to temperature sensors so fancontrol know which
	temperature sensors should be used for calculation of new values for
	the corresponding pwm outputs.

FCFANS
	FCFANS records the association between a pwm and a fan.
	Then fancontrol can check the fan speed and restart it if it
	stops unexpectedly.

MINTEMP
	The temperature at which the fan gets switched off completely.

MAXTEMP
	The temperature at which the fan gets switched to full speed.

MINSTART
	Sets the minimum speed at which the fan begins spinning. You should
	use a safe value to be sure it works, even when the fan gets old.

MINSTOP
	The minimum speed at which the fan still spins. Use a save value here,
	too.

If you set up your configuration by hand, be sure to include ALL variables and
use valid values, there's no error handling yet! The file format is a bit
strange:

VARIABLE=chip/pwmdev=value chip/pwmdev2=value2 [...] VARIABLE2=[...]

Each variable has its own line. The variable name is followed by an equal sign
and the device=value pairs. These consist of the relative path to the pwm
output (from /proc/sys/dev/sensors/) for which the value is valid, equal sign
followed by the value and are seperated by a blank.

Example:

MINTEMP=w83627hf-isa-0290/pwm2=40 w83627hf-isa-0290/pwm1=54

You have to play with the temperature values a bit to get happy. For initial
setup I recommend using the pwmconfig script. Small changes can be made by
editing the config file directly following the rules above.


The algorithm

fancontrol first reads its configuration, writes it to arrays and loops its
main function.  This function gets the temperatures and fanspeeds from
lm_sensors proc files and calculates new speeds depending on temperature
changes, but only if the temp is between MINTEMP and MAXTEMP. After that, the
new values are written to the pwm outputs.  Currently the speed increases
quadratically with rising temperature. This way you won't hear your fans most
of the time at best.


Planned features

rc-scripts for some gnu/linux-distributions
smoother regulation (temp interpolation)
other curve styles (linear, exponential)
gui for configuration

If you have other wishes or want to contribute something, please let me know:
marius.reiner${AT}hdev.de
